Method of preparing a zinc manganese ferrite



y 1962 L. w. BEAUDOIN ETAL 3,046,228

METHOD OF PREPARING A ZINC MANGANESE FERRITE Filed June 8, 1959 I7 NWWWW I8 52 [9mm IQZWW\/\/\/\ A51 40mm ZnO 30 31 32 33 34 35 as 37 3e 39 40 M10 INVENTORS LEONARD WIBEAUDOIN ATTORNEY RALPH e. KRAFT KENNETH W.STEINBRECHER United States Patent Ofiice Efidhi g Patented July 2 3 19%2 3,046,228 METHGD F PREPARING A ZINC MANGANESE FERRITE Leonard W. Beaudoin, lvfiliwaulree, Ralph G. Kraft,

Whitefish Bay, and Kenneth W. Steinhrecher, Shore- Wood, Wis, assignors to Allen-Bradley Company, Mil- Wauhee, Wis, a corporation of Wisconsin Filed June 8, 1959, Ser. No. 813,651 3 Claims. (Cl. 25262.5)

The present invention relates to ferromagnetic materials which essentially comprise a zinc manganese ferrite, and particularly relates to a ferrite composition for use as magnetic core materials for transformer cores, such as flybaclt transformers for television use and broad band and pulse transformers, wherein said materials provide a higher usable flux density and a core loss temperature coeflicient approaching zero or a negative value between room temperature and the usual operating temperature of the transformer.

In the early days of television, the horizontal defiection, or flyback transformers contained silicon steel laminated cores. The operating frequency of these transformers is 15.75 kc. p.s. during horizontal deflection and approximately 60 kc. p.s. during flyback; thus, it is quite obvious that to keep the core losses down, the laminated cores were necessarily built up of very thin laminations at great cost-to the transformer manufacturer. The development of powdered iron cores improved the flyback transformers considerably and also pointed the way to later improvements. The core losses of powdered iron at these frequencies were considerably lower than laminated cores, but the permeability was also very low, being at a value of about 100.

Ferrites later became commercially available which possessed both high permeability and low core losses. The early ferrites possessed rather low saturation inductions, and thus required special circuitry to fully utilize the high permeability and low core loss advantages. This was made necessary because the plate current for the horizontal deflection amplifier must pass through the transformer windings.

With the further development of larger and larger picture tubes, and the accompanying demands for more deflection power, it became necessary to improve the horizontal deflection circuitry. Thus, the conventional circuits began to incorporate the auto-transformer type winding which had certain advantages over the conventional transformer type winding; notably less copper was required, there was lower leakage inductance, lower distributed capacitance and improved efiiciency due to reduced copper losses. However, the advantages of the auto-transformer did not ease the core requirements, but placed even greater demands on the core material.

Since the auto-transformer has become quite universally accepted, it is advisable to examine briefly the magnetic properties pertinent to such application. First, the core losses must be considered at the operating flux density and te. iperature, as well as at the horizontal scanning frequency and the retrace frequency. Next, in the'operation of deflection transformers, a magnetic bias is present; thus, the influence of this bias on the permeability must be considered as well as the effect of temperature. We must also consider that a deflection transformer is definitely a high powered device and hence operation at high l'lux densities is necessary to prevent excessive core size. Thus, the core material must possess a high saturation induction at operation temperature.

To better understand the significance of desirable magnetic parameters provided by the present compositions, it is also desirable that we consider a part of the operation of a television ilyback transformer in which the present composition has found excellent application. For a fiyback transformer in operation the following conditions exist which influence the core:

(1) Two components of flux are present, an alternating and a DC. component;

(2) When the television set is turned on, the core will be operating at room temperature, but after a period of time, the temperature of the core will rise to possibly as high as C. (due to core losses, copper losses, and increasing ambient in the set caused by temperature rise of other components, such as tubes, resistors, etc.);

(3) During the retrace time of the cycle of operation high voltage is generated. The width and amplitude of the voltage pulse generated during retrace is governed primarily by the inductance and capacitance of the high voltage windings, as well as the copper losses and the core losses of the ferrite at the retrace frequency.

From the second and third conditions above, it will be apparent that the permeability of the core at the peak flux density must remain relatively constant with temperature. According to prior knowledge, the permeability of the core should not vary more than a factor of 2 to 1 between 25 C. and 115 for satisfactory operation. Usable flux density, B is a quality factor applied to ferrites for determining the usefulness of core material for use in fiyback transformers, and is defined as that flux density at which the 115 C. permeability is equal to one-half of the 25 C. permeability. It will be apparent that if the permeability is not to change more than 2 to 1 with temperature, that B then would be the highest value of flux density that can be used for a given material.

From the first condition above, it will be observed that the two components of flux exist; an A.C. component and a DC. component. The AC. component will be limited by the absolute value of core losses for a given material, whereas the DC. component would be limited by the value of B Thus it will be seen that B and ,u (,u. at B is defined as the permeability of the core at B measured at 25 C.) become very useful design parameters for the television fiyback transformer design engineer.

A temperature of 115 C. has been generally accepted by television manufacturers as the upper limit for the deflection transformer. For existing core materials this sets the upper limit of AC. flux density in the range 1000 Gauss to 2000- Gauss due to core losses. If there were no other components of flux than this A.C. flux, the only other requirements of the core would be a high permeability at this flux density which is stable up to 115 C. However, this is not the case, for we must also consider the DO bias. Here is where the parameters B and ,u. atB become important. For a given core material the sum of the A.C. and DC. fluxes must not exceed B Thus, in considering all of the factors in the design of a core material for purposes and use as in the cases of fiybacl; transformers and other applications in broad band and pulse transformers we have conceived of the ferrite composition comprising the present invention.

In the drawings:

FIG. 1 illustrates a ternary diagram of a zinc oxide, manganese oxide, iron oxide system illustrating the composition of the materials of the invention. in the diagram the various materials are expressed as mol percent of the total composition;

FIG. 2 is a perspective view of a typical toroidal core body made of a ferrite composition in accordance with the teachings of the present invention.

In accordance with the practice of the invention, suitable iron, manganese and zinc containing raw materials arereacted to form a ferromagnetic spinel when heated. Raw materials which have been found to be satisfactory acaaaas include hematite, mixtures of hematite and gamma-ferric oxide, manganese dioxide, manganese carbonate, manganous-manganic oxide and zinc oxide. The purity of the raw materials is considered important, and the total solid impurity content of the reacted ferrite should be substantially below one-half percent by weight. The selected materials are mixed in proportion, in terms of the appropriate metallic oxide, to form composition ranges lying within the area defined by the solid lines AB, BC, CD and DA of the ternary diagram of FIG. 1 of the drawing.

In evaluating various sample compositions comprising the area A, B, C, D on the diagram of FIG. 1, the composition designated by the point B on the diagram was found to exhibit particularly desirable properties, and

specimens during the heating portion of the cycle, and also during the first 2 hours of the soak at a soaking temperature of 2550 F. An atmosphere of nitrogen is thereafter flowed over the parts during the final hour of the soak period and also during cooling. The cooling rate used is in the range of 400 F. per hour to 600 F. per hour and the nitrogen used to provide a protective atmosphere may contain about 0.01% of oxygen.

After the sintering operation the magnetic properties of the ferrites may be measured.

Various magnetic measurements were made of finished ferrite samples designated E, F, G, H and I on the diagram of FIG. 1 to produce the results indicated in the following table:

TABLE I Table of Magnetic Properties Flux Core Loss, I ,W&ttS/Cm. c.p.s. Perme- Density, Test ability, B... at p. at Bu Composition Temp, [1m at 16 10 a., 16 kc. p.s. 60 kc. p.s. Bu 25 0.

C. kc. p.s. gauss at 16 kc. p s

1,350 g. 1,300 g. 1,350 g. 1,800 g.

comprised a composition of about 53.1 mol percent Fe O about 12.8 mol percent Z110 and about 34.1 mol percent MnO'. 1

The weighed raw materials from which, for instance, composition E may be prepared, comprise 63 parts by weight of Fe O 29 parts by weight of MnCO and 8 parts by weight of ZnO. The materials are admixed and are preferably ball milled together with distilled water for one hour. The mill is then discharged and the resulting slurry is dried at a temperature of 300 F. The dried material may be then screened to desired size and may be either molded into compacts, granulated, or pressed into refractory containers for subsequent heattreatment. The initial heat treatment, or calcining step, consists of heating the material to a temperature of 2225 F. in an air atmosphere and holding at this temperature for 2 hours, followed by cooling to room temperature. The reacted product is then jaw crushed to pass a 14 mesh screen and again introduced into a steel ball mill along with distilled water.

The batch is then milled until it becomes a desired size, which may range from between 1.25 to 1.35 microns, measured by means of a Fisher Sub Sieve Sizer, and again discharged for drying at a temperature of approximately 200 F.

The milled and dried ferrite material is next placed in a Muller type mixer and a binder material, such as emulsified wax with water providing to moisture, is then blended into the material until plastic consistency is obtained. The material is then granulated through a 30 mesh sieve and dried at a temperature of 180 F.

Toroidal specimens, such as the core 10 of FIG. 2

may be prepared by compacting the granulated ferrite in' steel molds at pressures ranging from 5 to 15 tons per square inch. After molding, the parts are slowly heated to 600 F. in a circulatory air atmosphere to remove the organic wax, and are cooled after remaining at this temperature' for several hours.

The dewaxed toroids are then placed on refractory tile for sintering and introduced into a tube furnace which is then sealed. The furnace is heated to a temperature of 2550 F. at a rate of 400 F. per hour and maintained at this temperature for 3 hours. Air is flowed over the As stated previously, the composition E is the preferred composition for use in flyback transformer application. This will be apparent on a single comparison of the diagram of FIG. 1 with Table I. It will be observed that as the iron content is increased from the relatively low amount of 51 mol percent of composition I, to the higher iron percentage of composition G, the level of core loss at 1800 gauss, 16 kc. p.s., decreases from a maximum value of approximately 8.60 for composition I to the considerably lower loss value of 2.89 for composition E, and then increasing again, as the iron proportion is increased, to a value of 5. 84 for composition G. It is also to be observed that, as the iron content is decreased from the amount of composition G, downwardly of the amount of composition E, to the amount of composition I, there is an improved temperature coeflicient characteristic of the core loss at 25 C. compared with the loss at C. In fact, the coefficient becomes negative at the composition I of less iron content. However, induction values also decrease with decrease of iron content, to thus make it preferable to choose a composition in the neighborhood of composition E.

It will be noted that this coeificient is positive for composition F having a core loss value of 5.0 1 at 25 C. and 6.60 at the operating temperature of 115 C., whereas, the composition E has a much less positive temperature coefiicient, indicating core loss values of 2.89 at 25 C. and 3.63 at 115 C. The temperature coefiicient is improved as the manganese oxide percentage is increased with a negative coefficient being exhibited by composition H having a core loss of 4.84 at 25 C. and 3.09 at 115 C. From a comparison of the test results of the various compositions it will also be observed that the core loss level goes through a trough as the manganese oxide content is increased. For instance, with reference to Table I, composition F exhibits a core loss level at 25 C. of a value of 4.59, whereas the loss level of composition E at 25 C. is 2.89, which loss level again increases with manganese content, to a value of 4.84 for composition H.

It will thus be apparent that a composition, such as the composition E, will provide desirable characteristics for use in flyback transformer application. However, it

will also be apparent from Table I that each of the various compositions defining the margins of the area A, B, C, D will provide desirable characteristics incident to greater usable flux density and high permeability accompanied by relatively low core loss.

Our investigation of ferrites made in accordance with the teachings of the present invention further indicated that a majority of the ferrites prepared were composed of grains or crystallites averaging in the order of 20 microns in size, but occasionally a part would be prepared which contained grains from several hundred to 1000 microns in size. The latter grains were of such size that could be easily measured by a simple ruler.

It was found that when all or most of a sintered ferrite was composed of large crystals, the magnetic losses were substantially higher than those of finer crystalline ferrite Also, as indicated in Table II, magnesium oxide, when added at a certain level to a zinc-manganese ferrite, made with high purity raw materials, has a pronounced effect on the magnetic core losses. Measured at 16 kc. p.s., 1800 gauss, the core losses of the ferrite increased with an increase in temperature from to 115 C. The addition of magnesium oxide, magnesium nitrate or magnesium carbonate, in terms of equivalent magnesium oxide, in an amount of 0.1%, by Weight, slightly increases the room temperature losses, but the 115 C. losses are correspondingly decreased. it Was also observed that amounts of magnesium oxide upwardly of 0.25% will continue to raise the room temperature core loss level to even a higher value.

It was also noted that there is little or no effect in adding magnesium oxide to commercially obtainable ma= terials. It appears that the various other impurities in such materials mask the effect of the magnesium compound.

It will be apparent that the present invention has provided anew and useful composition of matter, which composition has very beneficial use as a core material for transformer applications in the television field, and in other broad band and pulse type transformer applications.

TABLE II Table of Magnetic Properties Core Loss, p Watts/0111. c.p.s. Perme- Flux Test ability, Density, [L at B u Composition Temp. Ilm at 16 Bin at 10 16 kc. p.s. 60 kc. p.s. B 25 0 0. he. p.s. Oersted 1350 g. 1800 g. 1350 g. 1800 g.

Large Grain 25 5,330 4, 900 7.01 11. 6 15. 9 29. 6 2, 580 4,050 Structure. 115 3, 170 3, 720 11. 1 10.0 24. 0 44. 6

Microcrystal- 25 5, 970 4, 820 1. 65 3. 05 2. 93 5.50 2, 900 5, 090 line. 115 4, 880 3, 660 3. 63 6. 5.02 13. 3

Microerystalline with 25 6, 780 4, 700 2.06 3. 71 3. 04 6.05 3,000 5, 040 magnesium 115 5, 130 3, 500 2. 39 4. 37 5. l3 9. 46 additive.

It will be noted from Table I, that the core loss level We claim:

at 16 kc. p.s. is materially increased from a value of 3.05 in the microcrystalline structure to a value of 11.6 in the relatively large grain sample.

It was observed in the course of investigation of various samples of selected compositions that both the fine grained and the very coarse grained ferrites were obtained with materials of greater purity than the usual commercial raw materials used in the manufacture of ferrites. When commercial raw materials were used in the zinc-manganese ferrite, uniform intermediate-sized grains were produced. The magnetic losses resulting were higher than those exhibited when pure raw materials were used.

The appearance of coarse grains in ferrites made with higher purity raw materials is not always predictable, but can be produced by the addition of small amounts of certain impurities, such as compounds of sodium, barium and silica. The coarse-grains can be produced by impurities such as barium compounds either by adding the impurity to the ferrite batch prior to the forming of the specimen or by dusting the top surface of the specimen prior to sintering.

It was also found that the coarse-grained appearance develops on a ferrite made with high purity raw materials if the ferrite is held at the sintering temperature for an extended period of time. The development of the coarsegrained size on ferrites is believed to be associated with low but definite amounts of certain impurities.

1. The method of preparing a ferromagnetic zinc-manganese ferrite having a high usable flux density, low core loss and low core loss temperature coefficient comprising the steps of admixing a Zinc, a manganese and an iron compound in amounts, in terms of the respective oxides, consisting of relative mol percentages of ZnO, M and Fe O lying within the area defined approximately in the accompanying ternary diagram of FIG. 1 by the solid lines AB, BC, CD and DA; calcining said. admixture in an air atmosphere at a temperature of about 2225 F; milling the calcined mixture into a finely-divided particulate material; forming said material with an appropriate binder material into a desired shape; and sintering said formed material in an air atmosphere at a temperature of about 2550 F. for a period of approximately 2 hours, continuing said sintering at the said temperature for an additional hour in an atmosphere substantially devoid of oxygen to complete the chemical reaction of the various constituents and obtain desired densification thereof.

2. The method of preparing a ferromagnetic zinc-manganese ferrite core material having a high usable fiux density, low core loss and lowucore loss temperature coefficient comprising the steps of admixing a zinc, a manganese and an iron compound in amounts, in terms of the respective oxides, comprising about 53.1 mol percent of Fe O about 12.8 mol percent of ZnO, and about 34.1 mol percent of MnO; calcining said admixture in an air atmosphere at a temperature of about 2225 F.; milling the calcined mixture into a finely-divided particulate material; forming said material With anappropriate binder material into a desired shape; and sintering said formed material in an air atmosphere at a temperature for a period of approximately 2 hours, continuing said sintering at the said temperature for an additional hour in an atmosphere substantially devoid of oxygen to complete the chemical reaction of the various constituents and obtain desired densification thereof.

3. The method of preparing a ferromagnetic zinc-manganese ferrite having a high usable flux density, low core loss and low core loss temperature coeflicient comprising the steps of admixing a zinc, a manganese and an iron compound in amounts, in terms of the respective oxides, comprising relative mol percentages of ZnO, M110 and Fe O lying within the area defined approximately in the accompanying ternary diagram of FIG. 1 by the solid lines AB, BC, CD and DA; mixing with said admixture a magnesium compound in terms of equivalent MgO in an amount of between about 0.1% and 0.25% by Weight of total mix calcining said admixture in an air atmosphere at a temperature of about 2225 F.; forming said material with an appropriate binder material into desired shape; and sintering said formed material in an air atmosphere at a temperature of about 2550" F. for a period of approximately 2 hours, continuing said sintering at the said temperature for an additional hour in an atmosphere substantially devoid of oxygen to complete the chemical reaction of the various constituents and obtain desired densification thereof.

References Cited in the file of this patent UNITED STATES PATENTS 2,549,089 Hegyi Apr. 17, 1951 2,551,711 Snock et al. May 8, 1951 2,636,860 Snock et a1. Apr. 28, 1953 2,886,529 Guillaud May 12, 1959 2,958,664 Vassiliev et al. Nov. 1, 1960 2,960,472 Guillaud Nov. 15, 1960 FOREIGN PATENTS 1,120,702 France Apr. 23, 1956 1,128,416 France Apr. 27, 1956 1,137,488 France Jan. 14, 1957 1,171,294 France Sept. 29, 1958 OTHER REFERENCES Harvey et al.: RCA Review, September 1950, pp. 344- Fresh: Proceedings of the IRE, October 1956, pp. 1303- ,13 1 1. 

1. THE METHOD OF PREPARING A FERROMAGNETIC ZINC-MANGANESE FERRITE HAVING A HIGH USABLE FLUX DENSITY, LOW CORE LOSS AND LOW CORE LOSS TEMPERATURE COEFFICIENT COMPRISING THE STEPS OF ADMIXING A ZINC, A MANGANESE AND AN IRON COMPOUND IN AMOUNTS, IN TERMS OF THE RESPECTIVE OXIDES, CONSISTING OF RELATIVE MOL PERCENTAGES OFZNO, MNO AND FE2O3 LYING WITHIN THE AREA DEFINED APPROCIMATELY IN THE ACCOMPANYING TERNARY DIAGRAM OF FIG. 1 BY THE SOLID LINES AB, BC, CD AND DA; CALCINING SAID ADMIXTURE IN AN AIR ATMOSPHERE AT A TEMPERATURE OF ABOUT 2225*F.; MILLING THE CALCINED MIXTURE INTO A FINELY-DIVIDED PARTICULATE MATERIAL; FORMING SAID MATERIAL WITH AN APPROPRIATE BINDER MATERIAL INTO A DESIRED SHAPE; AND SINTERING SAID FORMED MATERIAL IN AN AIR ATMOSPHERE AT A TEMPERATURE OF ABOUT 2550*F. FOR A PERIOD OF APPROXIMATELY 2 HOURS, CONTINUING SAID SINTERING AT THE SAID TEMPERATURE FOR AN ADDITIONAL HOUR IN AN ATMOSPHERE SUBSTANTIALLY DEVOIF OF OXYGEN TO COMPLETE THE CHEMICAL REACTION OF THE VARIOU CONSTITUENTS AND OBTAIN DESIRED DENSIFICATION THEREOF. 